1. Field of the Invention
The present invention relates to a chemical sensor, and more particularly to a surface plasmon resonance biosensor for detecting a biosubstance, adapted for use in medical diagnosis, health checkup and food inspection.
2. Description of the Related Art
In the fields of medical diagnosis and food inspection, utilization of biosensors for detecting various physiological substances and biosubstances is advancing in recent years. In particular, various biosensors capable of detecting physiological substances and biosubstances of a small amount contained in a sample are being developed. Also desired is the development of a compact low-cost biosensor, capable of a high-speed sensing.
Also being developed is a biosensor for use in the detection of an antigen molecule utilizing an antigen-antibody reaction, and in the detection of a ligand molecule utilizing coupling of a ligand molecule with a receptor protein. Also in a biosensor executing detection by forming a composite substance of a capturing molecule, which specifically captures a physiological substance or a biosubstance constituting the target of detection, and such detection target substance, it is desired to achieve compactification, sensing performed at a higher speed and a low cost. A biosensor utilizing surface plasmon resonance as a transducer is considered promising for accomplishing compactification and measuring the amount of formed composite member precisely and within a short time. Such a surface plasmon resonance (SPR) biosensor, for example an SPR biosensor of Kretschmann construction, utilizes a metal thin film formed on the surface of a prism in such an arrangement that an incident light angle satisfies a total-reflection condition. Thus, there is utilized a surface plasmon resonance absorption (scattering), resulting from a coupling of a surface plasmon that is generated on the surface of the metal thin film disposed on the surface of the prism in such total-reflection arrangement and of incident light. A substance is adsorbed on the surface of the metal thin film, and a peak wavelength of the light inducing the surface plasmon resonance adsorption (scattering), namely the surface plasmon resonance wavelength, is shifted. A phenomenon that the shift amount of the surface plasmon resonance wavelength increases with an increase in the amount of substance adsorbed on the surface of the metal thin film, is utilized to measure the amount of the substance adsorbed on the surface of the metal thin film.
On the other hand, for the purpose of sensing of a high sensitivity, US 2003/0132392 proposes a localized surface plasmon resonance sensor utilizing a small aperture formed in the metal thin film. Such localized surface plasmon resonance sensor adopts a construction of irradiating the small aperture, formed in the metal thin film on a substrate, with a light, and measuring the transmittance of the light transmitted by the small aperture, thereby detecting a change in the medium in the vicinity of the small aperture.